Covering and assembly method for transcatheter valve

ABSTRACT

A covering layer for a transcatheter heart valve is in various embodiments configured to prevent or reduce damage to the native valve tissue around the site where the prosthetic valve is implanted. In some cases, prosthetic valves are manufactured with the covering layer attached. Other covering layers are stand-alone accessories that can be mounted onto pre-existing prosthetic valves by an end user. Covering layers that can be mounted by an end user are provided with various features that can facilitate easier attachment of the covering layer to the prosthetic valve, which further reduces the possibility of damage to the covering layer or to the valve. Another covering is provided with two layers in order to insulate and protect the native tissue surrounding the implant from damage due to friction or abrasion, and/or other movement driven wear.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/240,570, filed Aug. 18, 2016, which claims priority to and thebenefit of U.S. Provisional Patent Application Ser. No. 62/209,180,filed Aug. 24, 2015. Each of U.S. patent application Ser. No. 15/240,570and U.S. Provisional Patent Application Ser. No. 62/209,180 are herebyincorporated by reference in their entirety.

BACKGROUND Field

The invention relates generally to medical devices and procedurespertaining to prosthetic heart valves. More specifically, the inventionrelates to replacement of heart valves that have malformations and/ordysfunctions. Embodiments of the invention relate to prosthetic heartvalves for replacing a mitral valve in the heart, or for replacing othervalves where an additional ring or other anchor is utilized togetherwith the prosthetic heart valve at the implant site, and assemblymethods for preparing such prosthetic heart valves for implantation.

Description of Related Art

Referring first generally to FIGS. 1 and 2 , the mitral valve controlsthe flow of blood between the left atrium and the left ventricle of thehuman heart. After the left atrium receives oxygenated blood from thelungs via the pulmonary veins, the mitral valve permits the flow of theoxygenated blood from the left atrium into the left ventricle. When theleft ventricle contracts, the oxygenated blood held in the leftventricle is delivered through the aortic valve and the aorta to therest of the body. Meanwhile, the mitral valve closes during ventricularcontraction, to prevent the flow of blood back into the left atrium.

When the left ventricle contracts, the blood pressure in the leftventricle increases substantially, and urges the mitral valve closed.Due to the large pressure differential between the left ventricle andthe left atrium during ventricular contraction, a possibility ofprolapse, or eversion of the leaflets of the mitral valve back into theatrium, arises. To prevent this, a series of chordae tendineae connectthe mitral valve to the papillary muscles along opposing walls of theleft ventricle. The chordae tendineae are schematically illustrated inboth the heart cross-section of FIG. 1 and the top view of the mitralvalve in FIG. 2 . Just before and during ventricular contraction, thepapillary muscles also contract and maintain tension in the chordaetendineae, to hold the leaflets of the mitral valve in the closedposition and preventing them from turning inside-out and back into theatrium, thereby also preventing backflow of the oxygenated blood intothe left atrium.

Complications of the mitral valve can potentially cause fatal heartfailure. One form of valvular heart disease is mitral valve leak, alsoknown as mitral regurgitation, characterized by the abnormal leaking ofblood from the left ventricle back into the left atrium through themitral valve. In these circumstances, it may be desirable to repair themitral valve or to replace the functionality of the mitral valve withthat of a prosthetic heart valve.

Up to this point, mitral valve repair has been more popular than valvereplacement, since there were previously little or no effectivecommercially available ways to replace a mitral valve through catheterimplantation and/or other minimal or less invasive procedures.

Replacement of a mitral valve is difficult in many respects, forexample, due to the physical structure of the valve and difficulties inaccessing the valve. The most prominent obstacle for mitral valvereplacement is anchoring or retaining the valve in position, due to thevalve being subject to a large cyclic load. Especially duringventricular contraction, the movement of the heart and the load on thevalve can combine to shift or dislodge a prosthetic valve. Also, themovement and rhythmic load can fatigue materials, leading to fracturesof the implanted valve. If the orientation of a mitral prosthesis isunintentionally shifted, blood flow between the left atrium and the leftventricle can be obstructed or otherwise negatively affected. Whilepuncturing the tissue in or around the mitral valve annulus to betteranchor an implanted valve is an option for retaining the placement ofthe implant, this can potentially lead to unintended perforation of theheart and patient injury.

Another issue with mitral valve replacement is the size and shape of thenative mitral valve. A general shape of the mitral valve and itsleaflets as seen from the left atrium is illustrated in FIG. 2 . Themitral valve annulus is quite large and non-circular, when compared forexample, to the more circular aortic valve annulus, where valvereplacement is more prominent. As such, a circular prosthetic mitralvalve that is too small can cause leaks around the implanted valve(i.e., paravalvular leak) if a good seal is not established around thevalve. Meanwhile, a circular valve implant that is too large can stretchout and damage the native valve annulus.

SUMMARY

Since many valves have been developed for the aortic position, it wouldbe desirable to try to take advantage of these existing valvetechnologies and to utilize the same or similar valves in mitral valvereplacements. One way of utilizing these preexisting prosthetic valvesat the mitral position is to use the prosthetic valves together with ananchor or other docking station that will form a more appropriatelyshaped implant site at the mitral valve annulus, so that the prostheticvalves can be implanted more securely, while reducing or eliminatingleakage around the valve after implantation. For example, a mitralanchor or docking station can form a more circular bore to more closelymatch the circular profiles of existing valve implants. In this manner,an existing valve implant developed for the aortic position, perhapswith some modification, could then be implanted at the mitral positiontogether with such an anchor. Some existing valves can even fit wellwith little or no modification, such as the Edwards Lifesciences SapienXT™ valve.

Anchors or docking stations for anchoring prosthetic valves at themitral position can include, for example, rings or coils that wraparound portions of the native mitral valve or surrounding tissue, toform a more circular or cylindrical surface against which a prostheticvalve can expand. The anchors can wrap around, for example, the nativemitral leaflets, the chordae tendineae, and/or other surrounding tissue.Since the prosthetic heart valve is expanded inside the mitral valveannulus, native tissue is sandwiched between the valve frame and theanchor. The use of a prosthetic heart valve with a bare metal frame,together with an anchoring ring or coil, can lead to damage to thenative tissue that is pinched between the valve and the anchor. Forexample, friction between the surrounding native valve tissue with theapices, corners, or various other edges on the valve frame can damagethe tissue and lead, for example, to paravalvular leakage.

Features of the invention provide prosthetic heart valves that can beimplanted with existing anchors or docking stations at the mitralposition, and that will prevent or reduce damage to the surroundingnative valve tissue after implantation. Embodiments of the inventionprovide devices and methods for preparing prosthetic heart valves formitral valve replacement. The devices and methods can prevent or reduceregurgitation or leaking of blood around the replacement prosthesis atthe time of implantation, as well as prevent or reduce damage to thenative valve tissue over time, which will also lead to less paravalvularleakage in and around the implanted prosthesis long after the prostheticvalve has been implanted.

In an embodiment of the invention, a transcatheter heart valve includesa valve prosthesis including a radially expandable and collapsible frameand a plurality of valve leaflets positioned at least partially in theframe and configured to control blood flow through the valve prosthesis.The frame has a first end, a second end, and an outer surface extendingfrom the first end to the second end, and a covering connected to thevalve prosthesis. The covering covers at least the first end andsubstantially all of the outer surface of the frame.

In another embodiment of the invention, a covering is provided for avalve prosthesis including a frame and a plurality of valve leafletspositioned at least partially in the frame and configured to controlblood flow through the valve prosthesis, wherein the frame has a firstend defining an outflow end, a second end defining an inflow end, and anouter surface extending from the first end to the second end. Thecovering includes a covering layer configured to cover at least theouter surface of the frame at the first end and a plurality of stringsconnected to the covering layer, the strings configured to facilitateattachment of the covering layer to the valve prosthesis.

In yet another embodiment of the invention, a system includes a valveprosthesis including a radially expandable and collapsible frame and aplurality of valve leaflets positioned at least partially in the frameand configured to control blood flow through the valve prosthesis,wherein the frame has a first end defining an outflow end, a second enddefining an inflow end, and an outer surface extending from the firstend to the second end, and a covering separate from and attachable tothe valve prosthesis for covering at least the outer surface of theframe at the first end, the covering comprising at least one stringconfigured to facilitate attachment of the covering to the valveprosthesis.

In still another embodiment of the invention, a method is provided forattaching a covering on a valve prosthesis, the valve prosthesisincluding a frame and a plurality of valve leaflets positioned at leastpartially in the frame and configured to control blood flow through thevalve prosthesis, wherein the frame has a first end, a second end, andan outer surface extending from the first end to the second end, thecovering including a covering layer and a plurality of loops. The methodincludes mounting the covering layer around the outer surface of thevalve prosthesis and attaching the covering layer to the valveprosthesis using the plurality of loops.

According to embodiments of the invention, mitral valve replacement canbe more effectively realized by providing measures to better protect thesurrounding native valve tissue during and after implantation, through avariety of different implementation approaches.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparentfrom the description of embodiments using the accompanying drawings. Inthe drawings:

FIG. 1 shows a schematic cross-sectional view of a human heart;

FIG. 2 shows a schematic top view of the mitral valve annulus of aheart;

FIG. 3 shows a perspective view of an embodiment of a prosthetic heartvalve;

FIG. 4A shows a side cross-sectional view of a ring anchor deployed in amitral position of the heart, with an implanted valve prosthesis,according to an embodiment of the invention;

FIG. 4B shows a side cross-sectional view of a coil anchor deployed inthe mitral position of the heart, with an implanted valve prosthesis,according to another embodiment of the invention;

FIG. 5 shows a perspective view of the prosthetic heart valve of FIG. 3, with a casing or covering wrapped around the prosthesis, according toa first embodiment of the invention;

FIG. 6 shows a covering for a heart valve according to a secondembodiment;

FIG. 7 shows a perspective view of a prosthetic heart valve with thecovering of FIG. 6 wrapped around the prosthesis;

FIGS. 8A and 8B show a covering for a heart valve according to a thirdembodiment, before and after a final manufacturing step, respectively;

FIG. 9 shows a perspective view of a prosthetic heart valve with thecovering of FIGS. 8A and 8B wrapped around the prosthesis;

FIGS. 10A to 10C respectively show a perspective view, a close-up view,and a cross-sectional view of a portion of a covering for a heart valveaccording to a fourth embodiment;

FIG. 11 is a flow chart illustrating a method of assembling the coveringof FIGS. 10A-10C around a prosthetic heart valve according to the fourthembodiment of the invention;

FIG. 12 shows a step of assembling the covering around a prostheticheart valve according to the fourth embodiment;

FIG. 13 shows a step of attaching the covering around the prostheticheart valve according to the fourth embodiment;

FIG. 14 shows another step of attaching the covering around theprosthetic heart valve according to the fourth embodiment;

FIG. 15 shows a perspective view of a prosthetic heart valve with thecovering of FIG. 10A wrapped around the prosthesis;

FIG. 16 shows a perspective view of a prosthetic heart valve with acovering according to a fifth embodiment wrapped around the prosthesis;

FIG. 17 shows a side cross-sectional view of a ring anchor deployed in amitral position of the heart, with an implanted valve prosthesis coveredby the covering according to the fifth embodiment; and

FIG. 18 is an enlarged cross-sectional view of a portion of FIG. 17 ,showing a close-up of one side of the implanted valve prosthesis withthe covering according to the fifth embodiment.

DETAILED DESCRIPTION

Disclosed herein are prosthetic heart valves, and methods ofmanufacturing or preparing the prosthetic heart valves for implantation,that allow for prevention or reduction in damage to the native valvetissue surrounding the prosthesis or that come into contact with theprosthesis after implantation into a patient. By providing a more robustseal around the prosthetic implant, leakage in and around the implantcan be greatly reduced, and performance of the valve can be improved.

Some transcatheter heart valves are designed to be radially crimped tofacilitate endovascular delivery to an implant site at a patient'sheart. Once positioned at a native valve annulus, the replacement valveis then expanded to an operational state, for example, by an expansionballoon. One embodiment of a prosthetic heart valve is illustrated inFIG. 3 . A transcatheter heart valve with a valve profile similar to theprosthetic valve shown in FIG. 3 is the Edwards Lifesciences SAPIEN XT™valve. The prosthetic valve 1 in FIG. 3 has an inflow end 2 and anoutflow end 3, and includes a frame or stent 10 and a leaflet structure20 supported inside the frame 10. In some embodiments, a skirt 30 can beattached to an inner surface of the frame 10 to form a more suitableattachment surface for the valve leaflets of the leaflet structure 20.

The frame 10 can be made of any body compatible expandable material thatpermits both crimping to a radially collapsed state and expansion backto the expanded state illustrated in FIG. 3 . The frame 10 can also bemade of, for example, Nitinol or another self-expanding material. Othersuitable materials can also be used.

The frame 10 is an annular structure having a plurality of verticallyextending commissure attachment posts 11, which attach and help shapethe leaflet structure 20 therein. Additional vertical posts or struts12, along with circumferentially extending strut sections 13, help formthe rest of the frame 10. The strut sections 13 of the frame 10 zig-zagand form edged crown portions or apices 14 at the inflow and outflowends 2, 3 of the valve 1. Furthermore, the attachment posts 11 can alsoform edges at one or both ends of the frame 10.

In prosthetic valve 1, the skirt 30 is attached to an inner surface ofthe valve frame 10 via one or more threads 40, which generally wraparound to the outside of various struts 11, 12, 13 of the frame 10, asneeded. The skirt 30 provides a more substantive attachment surface forportions of the leaflet structure 20 positioned closer to the inflow end2 of the valve 1.

FIGS. 4A and 4B show side cross-sectional views of embodiments ofdifferent anchors that can be used to facilitate implantation of thevalve 1 at the mitral position of a patient's heart. As shown in FIGS.4A and 4B, a left side of a heart 80 includes a left atrium 82, a leftventricle 84, and a mitral valve 86 connecting the left atrium 82 andthe left ventricle 84. The mitral valve 86 includes anterior andposterior leaflets 88 that are connected to an inner wall of the leftventricle 84 via chordae tendineae 90 and papillary muscles 92.

In FIG. 4A, a first anchoring device includes a flexible ring or halo 60that surrounds the native leaflets 88 of the mitral valve 86 and/or thechordae tendineae 90. The ring 60 pinches or urges portions of theleaflets inwards, in order to form a more circular opening at the mitralposition, for more effective implantation of the prosthetic valve 1. Thevalve prosthesis 1 is retained in the native mitral valve annulus 86 bythe ring anchor 60, and can be delivered to the position shown, forexample, by positioning the valve 1 in the mitral annulus 86 while thevalve 1 is crimped, and then expanding the valve 1 once it is positionedas shown in FIG. 4A. Once expanded, the valve 1 pushes outwardly againstthe ring anchor 60 to secure the positions of both the valve 1 and thering anchor 60. In some embodiments, an undersized ring anchor 60 withan inner diameter that is slightly smaller than the diameter of theprosthetic valve 1 in its expanded state can be used, to providestronger friction between the parts, leading to more secure attachment.As can be seen in FIG. 4A, at least a portion of the native mitral valveleaflets 88 and/or a portion of the chordae tendineae 90 are pinched orsandwiched between the valve 1 and the ring anchor 60.

FIG. 4B is similar to FIG. 4A, except instead of a ring anchor 60, ahelical anchor 70 is utilized instead. The helical anchor 70 can includemore coils or turns than the ring anchor 60, and can extend bothupstream and downstream of the mitral valve annulus 86. The helicalanchor 70 in some situations can provide a greater and more secureattachment area against which the valve 1 can abut. Similar to the ringanchor 60 in FIG. 4A, at least a portion of the native mitral valveleaflets 88 and/or the chordae 90 are pinched between the valve 1 andthe helical anchor 70.

As discussed above, prosthetic valve 1 generally includes a metal frame10 that forms a number of edges. In addition, many frames 10 areconstructed with edged crowns or apices 14 and protruding commissureattachment posts 11, as well as threads 40 that can be exposed along anouter surface of the frame 10. These features can cause damage to thenative mitral tissue that is lodged between the prosthetic valve 1 andthe anchor 60, 70, for example, by movement or friction between thenative tissue and the various abrasive surfaces of the prosthetic valve1. In addition, other native tissue in close proximity to the prostheticvalve 1 can also potentially be damaged.

A prosthetic heart valve according to an embodiment of the invention isillustrated in FIG. 5 . FIG. 5 shows the prosthetic heart valve 1wrapped in a casing or covering 100. The covering 100 coverssubstantially an entire outer surface of the valve frame 10, so that thenative heart tissue around the valve prosthesis 1 is protected from thevarious edges and other abrasive surfaces of the valve 1, withoutaffecting functionality of the valve leaflets 20 housed inside the frame10. In one embodiment, the covering 100 is made of a biocompatible clothor other similar material. In another embodiment, pericardial tissue orpatches or other similar material can be used as the covering 100 tocover the entire valve 1 or portions of the outer surface of valve 1with exposed edges, abrasive materials, or other harmful surfaces. Suchcoverings 100 can be sewn or otherwise attached to the outside of thevalve frame 10, and can serve to reduce the friction between the valve 1and the surrounding native tissue at the implant site.

The covering 100 can be added to the outer surface of the prostheticvalve 1 during manufacturing. However, such an approach would involvechanging the manufacturing processes and equipment needed to make thevalve. Furthermore, adding a covering to existing valves at themanufacturing stage essentially creates a new valve that would likelyhave to undergo a new set of extensive and long term quality assuranceand regulatory testing before the valve can be brought to market. Thisapproach would be time consuming and incur a great deal of resources.

An alternative approach is provided in the embodiment illustrated inFIGS. 6 and 7 . FIGS. 6 and 7 show a second embodiment of the invention,which includes a casing or covering 200 that is a stand-alone accessorythat can be attached to an existing valve prosthesis by a practitioneror other end user. A main body 210 of the covering 200 can be made of abiocompatible cloth or other suitable biocompatible material with lowfriction and low abrasive properties. The cloth or other material usedfor the body 210 can be constructed of a stretchable material, possiblya knitted or otherwise breathable material, and/or a material that willpromote ingrowth after implantation. The body 210 of the covering 200 isa generally rectangular cloth with a central portion 211 sized andshaped to wrap around the entire prosthetic valve 1 in a circumferentialdirection. The body 210 further includes loop portions 212 on one orboth ends of the central portion 211, that will be positionedapproximate the inflow and outflow ends 2, 3 of the prosthetic valve 1.The loop portions 212 can be formed, for example, by folding over andsewing down or otherwise connecting the top and bottom ends of the body210 to form small overlapping regions defining sleeves or passageways.The loop portions 212 can also be formed using various other methods.The covering 200 further includes one or more strings or threads 220that are held in the loop portions 212 and that extend out of ends ofthe loop portions 212. Some embodiments of the covering 200 do notinclude loop portions 212, where the strings or threads 220 in theseembodiments are instead sewn directly to portions of the body 210, asneeded, in order to securely attach the threads 220 to the body 210.

As seen in FIG. 7 , the covering 200 can be wrapped or dressed around anouter surface of an existing prosthetic valve 1 by a practitioner orother end user, and ends of each of the threads 220 can be tightened andtied together using any appropriate suturing or tying technique, to keepthe covering 200 attached to the valve 1. The threads 220 can be used tofurther tighten the ends of the covering 200 so that the covering 200forms or defines slightly smaller or narrower end openings or perimetersthan the inflow and outflow ends 2, 3 of the valve 1. In this manner,the corners or apices 14 of the frame and/or ends of the commissureattachment posts 11 can also be covered by the covering 200, to betterprotect the surrounding heart tissue from being cut, abraded orotherwise damaged by the ends of the valve frame 10. In someembodiments, the end user can further sew or otherwise more securelyattach the meeting ends of the covering 200 with additional threads 230,to form an even more secure attachment between the covering 200 and thevalve prosthesis 1.

By providing a protective coat or covering 200 that is a separateaccessory according to the second embodiment shown in FIGS. 6 and 7 ,and that can be easily attached to an existing prosthetic valve 1 by apractitioner prior to implantation, the covering can more easily bebrought to market. Furthermore, coverings can be designed and modifiedin various different manners to facilitate easier attachment by endusers.

FIGS. 8A, 8B, and 9 show a third embodiment of the invention, whichincludes another coat or covering 300 that is a stand-alone accessoryattachable to an existing valve prosthesis by an end user. A main body310 of the covering 300 can be similar in size and shape to the mainbody 210 of the covering 200 in FIGS. 6 and 7 , and can be made of abiocompatible cloth or other material with similar properties as thosediscussed with respect to the body 210 of the covering 200. A length ofa central portion 311 of the body 310 of the covering 300 is sufficientfor circumferentially wrapping the covering 300 around the entireprosthetic valve 1.

The covering 300 differs from the covering 200 in FIGS. 6 and 7 in theconstruction of the attachment mechanisms for attaching the respectivecoverings to the prosthetic valve 1. Rather than the loop portions 212and the strings or threads 220, the covering 300 instead has an openfirst end 312 with a plurality of stringed or threaded loops 320attached thereto. A number and positioning of the loops 320 at the firstend 312 of the covering 300 can correspond to a number and position ofthe apices 14 located on one end of the valve frame 10, which in theillustrated embodiment, amounts to nine total loops 320. In anotherembodiment, the number and positioning of the loops 320 can correspondto the number and positions of the apices 14 and the protruding ends ofthe commissure attachment posts 11. In yet other embodiments, the numberand positioning of the loops 320 can vary and correspond, for example,to every other apex 14, or more generally, to the number and positionsof the desired attachment points between the first end 312 of thecovering 300 and the prosthetic valve 1, as described in greater detailbelow.

Meanwhile, another set of stringed or threaded loops 321 is positionedat an opposite second end 313 of the covering 300. The embodiment inFIGS. 8A to 9 includes nine loops 321 in addition to the nine loops 320located at the first end 312, but in other embodiments, the number andpositioning of the loops 321 can also be varied based generally on thepositions of the desired attachment points between the second end 313 ofthe covering 300 and the prosthetic valve 1. In addition, the second end313 of the covering is folded 314 and sewn or otherwise sealed together,so that loops 321 are at least partially covered or concealed within thefolded cloth or material. In some embodiments, the loops 321 are coveredcompletely by the folded portion. In other embodiments, rather than afolded portion, the loops 321 at the second end 313 of the covering 300can instead by covered by an additional piece of cloth or material thatis separately attached to the body 311 of the covering 300.

As shown in FIG. 9 , the covering 300 can be wrapped or dressed aroundthe outer surface of an existing prosthetic valve 1 by a practitioner orother end user. In this embodiment, the loops 320, 321 can be fittedover corresponding apices 14 or protruding ends of the commissureattachment posts 11 on the valve frame 10. The covered loops 321 at thesecond end 313 of the covering 300 can first be fitted over the apices14 or other frame protrusions at the outflow end 3 of the prostheticvalve 1, and then the uncovered loops 321 can be fitted over the apices14 or other frame protrusions at the inflow end 2 of the prostheticvalve 1. In another attachment method, loops 321 at the second end 313and loops 320 at the first end 312 can be alternately attached to theprosthetic valve. Other attachment methods can, of course, also be used.

A vertical height of the covering 300 (i.e., between the first andsecond ends 312, 313 of the covering 300) can be slightly shorter than aheight of the valve prosthesis 1, so that the covering 300 stretches ina vertical direction when the loops 321 and 320 are both attached to theframe 10, in order to form a more tight or secure connection between thevalve 1 and the covering 300. Meanwhile, the loops 321 at the second end313 are at least partially covered or concealed, so that the valve framecan be attached to the loops 321 at an inner side of the covering 300.In this manner, the second end 313 of the covering can also betterconceal or cover apices and other valve frame edges at the outflow end 3of the valve 1. Referring back to FIGS. 4A and 4B, the outflow end 3 ofthe valve 1 is positioned in the left ventricle 84, and will be the endof the valve 1 that comes into contact with the native mitral valveleaflets 88. Therefore, the covered loops 321 at the second end 313 ofthe covering 300 will be more effective in covering the apices 14 andother edges at the outflow end 3 of the valve 1 and in protecting thenative valve leaflets 88 and other surrounding heart tissue from beingdamaged by the valve 1. On the other hand, the loops 320 at the firstend 312 of the covering 300 correspond to the inflow end 2 of the valve1, which is positioned in the left atrium 82 after implantation. Sincethe inflow end 2 of the valve 1 is spaced farther apart from any hearttissue, there is less concern that the apices 14 or other sharp edges atthe inflow end 2 will damage the surrounding tissue. The loops 320configured to be attached to the inflow end 2 of the valve 1 cantherefore be more exposed, for example, to facilitate easier access andfor easier attachment of the loops over the apices 14 and/or otherprotrusions at the inflow end 2 of the valve 1 by the end user. Theloops 320, 321 can simply be fitted over a corresponding apex or edge ofthe valve frame with a single looping, or for example, each of the loops320, 321 can be folded over to form multiple loopings around the apicesfor a more secure fit.

After attachment of the loops 320, 321 to the various protrusions at theends 2, 3 of the prosthetic valve 1, in some embodiments, the end usercan then further sew or otherwise more securely attach the meeting endsof the covering 300, for example, as seen in FIG. 7 , to form an evenmore secure attachment between the covering 300 and the valve prosthesis1. In some embodiments, ends of the covering 300 can be sewn togetherfirst, to form a tubular or substantially cylindrically shaped covering300, into which the valve prosthesis 1 can be inserted, where attachmentof the loops 321, 320 would then proceed similarly as previouslydiscussed.

In some embodiments, the various attachment features discussed in thesecond embodiment of FIGS. 6 and 7 and in the third embodiment of FIGS.8A, 8B, and 9 can be combined into a single covering, where for example,one end of the covering includes a loop portion with a string or threadsimilarly as discussed in the second embodiment, and the other end ofthe covering includes a plurality of loops to fit over protrusions at anend of the valve prosthesis 1. Various other modifications can also beenvisioned based on, for example, the specific needs and desiredproperties of the patient and the prosthetic valve to be implanted.

In some embodiments, in addition to making attachments to an existingvalve prosthesis only at the top and bottom ends of the valve, apractitioner may want to more securely attach a covering or wrap aroundthe valve prosthesis with, for example, additional sutures or stringties at other positions on the valve frame of the prosthetic. Generally,threading strings or sutures through a valve and another layer prior totying the layer down to the valve frame involves using a needle or othersharp tool that can pierce through the extra layer. However, use of aneedle or other sharp tools around the outflow area of the valveprosthesis by an end user might lead to unintended cuts, punctures, orother damage to the valve leaflets. Such damage is also difficult toforesee or predict by the manufacturer, and can also be difficult todetect by the end user even when it occurs.

FIGS. 10A to 10C show a fourth embodiment of the invention, whichincludes another coat or covering 400 that is a stand-alone accessoryattachable to an existing valve prosthesis by an end user. The covering400 according to the fourth embodiment includes a plurality ofpre-positioned loops that are intended to serve as a substitute forusing a needle to thread or transmit strings or sutures therethrough, toaid in attaching the parts together by an end user. Sutures or stringscan be threaded through the covering by first inserting the suturesthrough the loops on one side of the covering 400, and then pulling theloops through the covering to also transmit or thread the attachedsutures through the covering 400 as well.

Referring to FIGS. 10A to 10C, a main body 410 of the covering 400 canbe similar in size, shape, and construction to either the main body 210of the covering 200 discussed in FIGS. 6 and 7 , or the main body 310 ofthe covering 300 discussed in FIGS. 8A, 8B, and 9 , or can be acombination including features from each covering. The body 400 can bemade of a biocompatible cloth or other suitable material with similarproperties as those previously discussed, and a length of the centralportion 411 of the body 410 of the covering 400 is sufficient to wrapthe covering 400 around the entire prosthetic valve 1 in acircumferential direction. In some embodiments, the covering 400 can bepre-manufactured and delivered to an end user with the side ends alreadysewn or otherwise attached together, such that the covering 400 isprovided to the end user in a substantially cylindrical shape, as can beseen for example in FIG. 12 . In other embodiments, the ends of thecovering 400 can be sewn or otherwise attached together by an end userduring the assembly of the covering 400 onto a prosthetic valve 1,similarly as discussed with respect to previous embodiments. Forexample, in the embodiment illustrated in FIG. 10A, the covering 400includes loop portions 412 and end strings 420 that can be used toconnect ends of the covering 400, similar to features discussed withrespect to the covering 200 above.

The covering 400 further includes a plurality of individually threadedloops 430 that are separately threaded through the body 410 of thecovering 400 during manufacturing, or at some other time prior to thecovering 400 being provided to the end user. Each of the threaded loops430 can be a separate loop made of string or of any other suitablematerial, and is threaded through a corresponding opening 413 at aspecific position on the body 410 of the covering 400. The number andposition of the openings 413 and positioning of the loops 430corresponds to desired positions through which strings or sutures areintended to traverse through the covering 400 to facilitate attachmentof the covering 400 to a frame 10 of a valve prosthesis 1. In otherwords, the loops 430 are positioned through openings 413 in the body 410of the covering 400 in at least some positions (and in some cases, allof the positions) where an end user will form a connection point betweenthe frame 10 and the covering 400. Therefore, different embodiments willinclude a different number of loops 430 and/or different positioning ofthe loops 430, based on the valve prosthesis and/or where the additionalconnection points are desired. In this manner, an end user can reduce oreliminate the need for a needle or other sharp tool, and thereby reducethe potential for damage caused by such a tool, during attachment of thecovering 400 to the prosthetic valve 1.

FIG. 11 is a flow chart illustrating a method of assembling the covering400 around a prosthetic heart valve. First, in step S101, the wrap orcovering 400 is separately prepared before attaching the covering 400 tothe valve 1. Generally, the covering 400 will be held in dry storage, sopreparation can include, for example, removing the covering 400 frompackaging and soaking the covering 400 in saline, water or othersolution to soften the covering 400. In embodiments where ends of thecovering 400 have not yet been joined, the end user can join the ends ofthe covering 400. The covering 400 can then be manipulated and adjustedor shaped into a substantially cylindrical form, as can be seen in FIG.12 . In addition, the various strings or sutures that are held in thecovering 400 can be moved or adjusted to allow for easier insertion ofthe prosthetic valve 1 and to avoid tangling between the various stringsor sutures.

In step S102, the prosthetic valve 1 is inserted into the covering 400through one end of the covering 400 to mount the covering 400 over thevalve 1, and in step S103, the loops 430 of the covering 400 arepositioned through the openings in the valve frame 10 at desiredlocations (e.g., a separate loop 430 can be positioned on each side of astrut or apex around which a suture is to be tied). In one embodiment,the loops 430 are positioned around select middle apices of the valveframe 10 that are located around the outflow end 3 of the valve 1. Insome embodiments, end attachment features can also be utilized to attachthe ends of the covering 400 over or around the ends of the valve frame10. Such attachment features can be similar to those discussed withrespect to the second or third embodiments above, or can include variousother end attachment methods, and can be employed before, during, orafter positioning of the loops 430. Generally, the pieces of string orsuture associated with end attachment will be trimmed and discardedprior to using the additional loops 430.

In step S104, and as can be seen in FIG. 13 , tie down threads orsutures 440 are inserted through the loops 430 at an inner side of valveframe 10. The size of the portions of the loops 430 located on the innerside of the valve frame are large enough to facilitate easy insertion ofthe threads or sutures 440 through the loops 430 by an end user, withoutthe use of any additional tools.

In step S105, and as can be seen in FIG. 14 , while the threads orsutures 440 are threaded through the loops 430, each of the loops 430 ispulled from the outside of the covering 400 radially away from thecovering 400 until the loops 430 are separated or detached from the body410 of the covering 400. In this manner, each of the sutures 440 ispulled with its corresponding loop 430 through the covering 400, and thesutures 440 can now be accessed from the outside of the assembly,without the use of a threading needle or other sharp tool. Afterthreading or transferring a portion of a suture 440 through the covering400, the corresponding loop 430 can be detached from the suture 440 anddiscarded. In some embodiments, it can also be desirable to thread ortransfer a suture 440 from an outer side of the assembly through thecovering 400 to an inner side of the assembly. The loops 430 can beutilized to facilitate transfer of sutures 440 in this direction aswell. After the sutures 440 have been threaded through the covering 400at the desired positions, and the loops 430 have been discarded, the enduser can also verify that none of the strings are tangled beforeproceeding.

In step S106, the sutures 440 are tied down 441 (see FIG. 15 ) at thecorresponding connection points using any appropriate tying or suturingtechnique, to more securely attach the covering 400 to the valve frame10, and the excess strings or sutures can be trimmed away. In someembodiments, the sutures 440 can be individually tied down arounddesired struts, posts, or apices of the valve frame 10, while in otherembodiments, more complex tying or suturing methods can be employed, forexample, to also interweave separate sutures 440 or to apply a singlesuture 440 around multiple struts and/or apices of the valve frame 10.The type of attachment method utilized can be varied based on theproperties of the covering 400 and the valve 1, and the level ofattachment between the covering 400 and the valve frame 10 desired bythe practitioner. In other embodiments, additional sutures are moresparingly applied, and these embodiments can include or incorporate useof a smaller number of loops 430, to simplify the assembly process forthe end user, and for example, to reduce possibility of the strings orsutures crossing or tangling.

In step S107, final preparation of the valve assembly prior toimplantation is performed. For example, the positioning of the covering400 on the valve 1 can be checked and verified, and minor adjustmentscan be made to the position of the covering 400, to ensure that theapices 14, portions of the commissure attachment posts 11 that formprotrusions, and any other ends or edges of the valve frame 10 arepositioned correctly in pockets of the covering 400 and/or are otherwiseadequately concealed or covered by the covering 400. Meanwhile, thepreviously discussed end attachments can also be supplemented. Forexample, as the loops 430 are generally employed for the portion of thecovering positioned around the outflow end 3 of the valve 1, thepractitioner can go back to the inflow end 2 of the valve 1, to ensurethat the covering 400 is still correctly positioned at inflow end 2after the sutures 440 have been applied at the outflow end 3. In someembodiments, additional sutures can also be made at the inflow end tofurther supplement the connection. The sutures at the inflow end 2 canin some instances be made using a needle or other sharp tool, since thesutures are made through the skirt 30 rather than the leaflet tissue 20,and so damage to the leaflet tissue 20 at the inflow end 2 is lesslikely. An example of a completed valve assembly, with a prostheticvalve 1 wrapped by a covering 400, is illustrated in FIG. 15 . The tieddown sutures 441 are exaggerated in FIG. 15 for clarity, and toillustrate example positions of the additional suture connectionsbetween the valve frame 10 and the covering 400.

In step S108, the covered valve assembly can be mounted onto a deliverysystem and crimped to prepare the valve assembly for implantation into apatient. Due to the addition of the covering 400, crimping of the valveassembly can be modified to avoid damaging covering 400 or detachment ofthe covering 400 from the valve 1. In one embodiment, the valve 1 ispre-crimped to an intermediate size (e.g., to a 24 mm outer diameter)before attachment of the covering 400 over the valve 1, and is thencrimped to its final crimped state after attaching the covering 400. Thefully crimped valve 1 with the covering 400 can then be delivered to theimplant site.

Using a covering with loops according to the fourth embodiment canreduce the time it takes to thread or transmit sutures from one side ofthe valve frame and covering to the other side of the valve frame andcovering. Furthermore, the suturing process becomes easier and quickerfor the end user, because the sutures only need be threaded through thelarge loops instead of through an eye of a needle or other sharpthreading tool, and use of sharp tools around the valve leaflet tissueis no longer necessary, eliminating the possibility of unintended damageto the leaflets caused by any such sharp tools, and thereby improvingthe overall performance of the implanted valves in general. In addition,since the loops are threaded through and pre-positioned on the coveringduring manufacturing, accuracy of the through holes for the sutures canbe pre-set, leading to more accurate placement of the sutures and lesserrors.

While the above embodiments better protect the tissue surrounding theprosthetic valve implant from being damaged by the edges or abrasivesurfaces of the implant, other issues can still arise both during andafter implantation of the valve prosthesis at the mitral position. Forexample, during deployment and expansion of the valve prosthesis, theprosthesis generally comes into contact with the native mitral valveleaflets and/or the chordae tendineae, and in some instances, comesdirectly into contact with the ring or coil anchor, before the valve isfully expanded. Further expansion of the valve inside the ring or coilanchor after such contact will therefore apply outwardly directed radialpressure against, and slightly expand, the ring or coil anchor as well,leading to circumferential shifting or sliding between the valve frameand the ring or coil anchor. This can subject the native valve tissue orother heart tissue sandwiched between the valve frame and the anchor toabrasion oriented damage in the circumferential direction. Furthermore,after implantation of the valve prosthesis, typical pressures applied tothe valve during regular heart cardiac cycles can also induce smallmovements of the valve in an axial direction relative to the ring orcoil anchor, which can also cause accelerated wear of the tissuesandwiched between the valve frame and the anchor. Even with coveringssimilar to those discussed in previous embodiments, these issues may notbe fully alleviated, since if the coatings or wraps are applied tightlyto an outer surface of the prosthetic valve, friction can still occurbetween the coating or wrap, the ring or coil anchor, and any tissuesandwiched therebetween, which can still lead to damage to thesandwiched native tissue.

FIG. 16 shows a fifth embodiment of the invention, which includesanother coat or covering 500. In some embodiments, the covering 500 isattached to the prosthetic valve 1 during the manufacturing process, butin other embodiments, the covering 500 can be modified to be astand-alone accessory that is attachable to an existing valve prosthesisby an end user. The covering 500 is configured to wrap around and tocover substantially the entire valve frame 10. The covering 500 can bemade of a biocompatible cloth or other material with similar propertiesas those discussed in the previous embodiments.

The covering 500 in FIG. 16 differs from previously discussedembodiments in that the covering 500 is a dual layer covering, where afirst layer of cloth can be tightly attached to and around the valveframe 10, while a second layer of cloth rests on an outer surface of thefirst layer of cloth. A cross-section of the two layers of covering 500is more clearly illustrated in FIGS. 17 and 18 . In one arrangement, thetwo layer covering can be formed by a tubular body that is attached atthe free ends. In another arrangement, two separate layers of cloth canbe stacked and then sewn or otherwise attached together, where the twolayers are sized and attached in a manner that facilitates easy slidingmovement between the layers. The first or inner layer of the coveringcan be attached to the valve frame in a tight manner, while the secondor outer layer of the covering can be arranged or attached on an outersurface of the first layer more loosely, or in any other way that allowsthe second layer to slide, at least to a limited extent, relative to thefirst layer.

FIGS. 17 and 18 more clearly illustrate the interactions between the twolayers of the dual-layer covering 500 according to the fifth embodiment.FIG. 17 illustrates a prosthetic valve with the covering 500 deployed ina ring anchor 60 positioned around native leaflets 88 of a mitral valve86, similarly as seen in FIG. 4A. A similar covered valve can also beused together with coil anchor 70 discussed with respect to FIG. 4B, orwith any other similar anchor. As can be seen in FIG. 17 , the covering500 is noticeably longer than the prosthetic valve 1 in the axialdirection, such that portions of the covering 500 extend axially awayfrom ends of the valve 1 in one or both directions.

FIG. 18 shows a close-up cross-sectional view of one side of the valveframe 10, the anchor 60, and a portion of the native mitral valveleaflets 88 sandwiched therebetween. A first layer 501 of the covering500 is attached to an outer surface of the valve frame 10, using one ofvarious attachment methods, for example, any of the attachment methodsdiscussed in the previous embodiments. Meanwhile, a second layer 502 ofthe covering 500 is positioned on an outer surface of the first layer501, and also comes into contact with and is pushed up against thenative mitral valve leaflets 88, the chordae tendineae, and/or othersurrounding native heart tissue. Some portions of the second layer 502of the covering 500 can also directly contact the anchor 60. Radialoutward pressure applied by the expanded prosthetic valve 1 against thecovering 500, the anchor 60, and the sandwiched tissue 88 causes africtional attachment of the second layer 502 against the tissue and/orthe anchor 60, such that relative movement between the second layer 502with the tissue and/or the anchor 60 is minimized or prevented.Meanwhile, a sliding plane or interface is formed between the firstlayer 501 and the second layer 502 of the covering 500, where slidingbetween the layers 501, 502 is still permitted, and can be facilitated,for example, by an additional layer or substance added between the firstlayer 501 and the second layer 502 that reduces friction, or forexample, by selecting a material for the covering where layers of thematerial slide easily against one another, or by any other suitablemeans.

The first layer 501 of the covering 500 remains affixed or pushed upagainst an outer surface of the valve frame 10, while the second layer502 of the covering 500 remains generally affixed or pushed up againstthe native valve or other heart tissue 88 and/or the anchor 60. Whenmicro movements or other small movements between the valve prosthesis 1and the anchor 60 occurs in any direction, the two layers 501, 502 ofthe covering 500 slide against one another, thereby absorbing themovements of the valve 1 relative to the anchor 60 and the sandwichedtissue 88. In this manner, relative movement between the tissue 88 andeach of the parts of the implant with which it comes into contact (e.g.,the second layer 502, the anchor 60, etc.) is minimized or eliminated,so that abrasive conditions due to friction or other rubbing or movementagainst the tissue 88 will also be minimized, and thereby reducingdamage to the tissue 88. Using a dual layer covering 500 according tothe fifth embodiment can therefore isolate and protect the tissue 88sandwiched between the valve 1 and the anchor 60 from small movementsthat could cause abrasive pressure, movement driven wear, and/or othersimilar damage to the tissue 88.

In other embodiments, various features from the different embodimentsdiscussed above can also be combined into a single valve prosthesis, orinto a stand-alone wrap or covering that can be assembled onto a valveprosthesis by an end user. In addition, various other modifications oralternative configurations can be made to the valve prostheses and/orthe stand-alone wraps or coverings according to the above describedembodiments of the invention. For example, the attachment featuresand/or methods for attaching the covering to the prosthetic valves canbe modified to attach to different prosthetic valves or to differentparts of the same valves, or for example, the single and dual layercoverings can be manufactured in different ways and using differentmaterials from those discussed above. The covered valves can also beused together with other types of rings or anchors, other parts orfeatures that define a bore or space into which the valve expands, or insome cases, the valves can be implanted directly in the native valveannuli without any additional anchors or other structural supportingparts or features.

For purposes of this description, certain aspects, advantages, and novelfeatures of the embodiments of this disclosure are described herein. Thedisclosed methods, apparatus, and systems should not be construed asbeing limiting in any way. Instead, the present disclosure is directedtoward all novel and nonobvious features and aspects of the variousdisclosed embodiments, alone and in various combinations andsub-combinations with one another. The methods, apparatus, and systemsare not limited to any specific aspect or feature or combinationthereof, nor do the disclosed embodiments require that any one or morespecific advantages be present or problems be solved.

Although the operations of some of the disclosed embodiments aredescribed in a particular, sequential order for convenient presentation,it should be understood that this manner of description encompassesrearrangement, unless a particular ordering is required by specificlanguage set forth below. For example, operations described sequentiallycan in some cases be rearranged or performed concurrently. Moreover, forthe sake of simplicity, the attached figures may not show the variousways in which the disclosed methods can be used in conjunction withother methods. Additionally, the description sometimes uses terms like“provide” or “achieve” to describe the disclosed methods. These termsare high-level abstractions of the actual operations that are performed.The actual operations that correspond to these terms can vary dependingon the particular implementation and are readily discernible by one ofordinary skill in the art.

In view of the many possible embodiments to which the principles of thedisclosure can be applied, it should be recognized that the illustratedembodiments are only preferred examples and should not be taken aslimiting the scope of the disclosure. Rather, the scope of thedisclosure is defined by the following claims.

What is claimed is:
 1. A prosthetic heart valve, comprising: a radiallyexpandable and collapsible frame having an inflow end and an outflowend, and comprising a plurality of apices; a plurality of valve leafletspositioned at least partially in the frame and configured to controlblood flow through the prosthetic heart valve; and a covering disposedaround the frame, the covering comprising a first end adjacent theinflow end of the frame and a second end adjacent the outflow end of theframe, the covering comprising a plurality of pre-positioned string,thread, or suture loops fitted over apices of the frame such that thecovering and the plurality of pre-positioned string, thread, or sutureloops are attachable to and separable from the frame as a standaloneaccessory; wherein each of the pre-positioned string, thread, or sutureloops comprises a separate piece of string, thread, or suture attachedto the second end of the covering; and wherein the plurality ofpre-positioned string, thread, or suture loops are held between a firstlayer of the covering and a second layer of the covering.
 2. Theprosthetic heart valve of claim 1, wherein the second end of thecovering is folded together so that the plurality of pre-positionedstring, thread, or suture loops are at least partially covered withinthe folded second end of the covering.
 3. The prosthetic heart valve ofclaim 1, wherein the frame is attached to the plurality ofpre-positioned string, thread, or suture loops at an inner side of thecovering such that the covering covers apices of the frame at theoutflow end of the frame.
 4. The prosthetic heart valve of claim 1,wherein: the plurality of pre-positioned string, thread, or suture loopsattached to the second end of the covering is a first plurality ofpre-positioned string, thread, or suture loops; and the covering furthercomprises a second plurality of pre-positioned string, thread, or sutureloops attached to the first end of the covering.
 5. The prosthetic heartvalve of claim 1, wherein a vertical height of the covering between thefirst and second ends of the covering is shorter than a height of theframe.
 6. The prosthetic heart valve of claim 1, wherein the coveringcomprises a cloth layer.
 7. The prosthetic heart valve of claim 1,wherein the covering comprises pericardial tissue.
 8. The prostheticheart valve of claim 1, wherein the covering further comprises aplurality of separable pre-positioned string, thread, or suture loopsthat are separable from the covering and positioned through openings ofthe covering such that at least a portion of each separablepre-positioned string, thread, or suture loop is positioned on each sideof the covering.
 9. The prosthetic heart valve of claim 1, wherein twoends of the covering are attached to one another such that the coveringforms a tubular structure.
 10. A prosthetic heart valve, comprising: aradially expandable and collapsible frame having an inflow end and anoutflow end, and comprising a plurality of apices; a plurality of valveleaflets positioned at least partially in the frame and configured tocontrol blood flow through the prosthetic heart valve; and a coveringdisposed around the frame, the covering comprising a first end adjacentthe inflow end of the frame and a second end adjacent the outflow end ofthe frame, the covering comprising a plurality of pre-positioned string,thread, or suture loops attached to the second end of the covering suchthat the covering and the plurality of pre-positioned string, thread, orsuture loops are attachable to and separable from the frame as astandalone accessory, the pre-positioned string, thread, or suture loopsbeing on an inner side of the covering and fitted over frame apices atthe outflow end of the frame such that the covering covers the frameapices at the outflow end of the frame; wherein each of thepre-positioned string, thread, or suture loops comprises a separatepiece of string, thread, or suture, and wherein the plurality ofpre-positioned string, thread, or suture loops are held between a firstlayer of the covering and a second layer of the covering.
 11. Theprosthetic heart valve of claim 10, wherein the second end of thecovering is folded together so that the plurality of pre-positionedstring, thread, or suture loops are at least partially covered withinthe folded second end of the covering.
 12. The prosthetic heart valve ofclaim 10, wherein: the plurality of pre-positioned string, thread, orsuture loops attached to the second end of the covering is a firstplurality of pre-positioned string, thread, or suture loops; and thecovering further comprises a second plurality of pre-positioned string,thread, or suture loops attached to the first end of the covering. 13.The prosthetic heart valve of claim 10, wherein a vertical height of thecovering between the first and second ends of the covering is shorterthan a height of the frame.
 14. The prosthetic heart valve of claim 10,wherein the covering further comprises a plurality of separablepre-positioned string, thread, or suture loops that are separable fromthe covering and positioned through openings of the covering such thatat least a portion of each separable pre-positioned string, thread, orsuture loop is positioned on each side of the covering.
 15. Theprosthetic heart valve of claim 10, wherein two ends of the covering areattached to one another such that the covering forms a tubularstructure.
 16. A prosthetic heart valve, comprising: a radiallyexpandable and collapsible frame having an inflow end and an outflowend, and comprising a plurality of apices; a plurality of valve leafletspositioned at least partially in the frame and configured to controlblood flow through the prosthetic heart valve; and a covering disposedaround the frame, the covering comprising a first end adjacent theinflow end of the frame and a second end adjacent the outflow end of theframe, the covering comprising a first plurality of pre-positionedstring, thread, or suture loops at the first end fitted over inflowapices of the frame and a second plurality of pre-positioned string,thread, or suture loops at the second end fitted over outflow apices ofthe frame, the second end of the covering being folded together so thatthe second plurality of pre-positioned string, thread, or suture loopsare at least partially covered within the folded second end of thecovering.
 17. The prosthetic heart valve of claim 16, wherein two endsof the covering are attached to one another such that the covering formsa tubular structure.
 18. A method of mounting the covering to theprosthetic heart valve of claim 1, comprising: wrapping the coveringaround the frame; and fitting the plurality of pre-positioned string,thread, or suture loops over apices of the frame to secure the coveringto the frame.
 19. A method of mounting the covering to the prostheticheart valve of claim 10, comprising: wrapping the covering around theframe; and fitting the plurality of pre-positioned string, thread, orsuture loops over the frame apices of the frame to secure the coveringto the frame.
 20. A method of mounting the covering to the prostheticheart valve of claim 16, comprising: wrapping the covering around theframe; and fitting the plurality of pre-positioned string, thread, orsuture loops over the inflow and outflow apices of the frame to securethe covering to the frame.